This project is designed to monitor the occurrence and induction of multiple forms of microsomal cytochrome P-450 at various ages in rabbits. Four forms of hepatic microsomal cytochrome P-450 have been isolated and characterized. Properties of these cytochromes such as immunoreactivity, molecular weights, and peptide fingerprinting can be used to distinguish each form and identify their occurrence in microsomes. Immunochemical techniques are being developed to provide quantitative information regarding the ontogenetic expression of each form and to localize the cytochromes in tissues histologically. These studies are designed to explore the relationship between the age-dependent occurrence of multiple forms of cytochrome P-450 and the balance between xenobiotic activation and detoxification catalyzed by the cytochromes.